Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Whether Photons Do In Fact Age

  1. Feb 25, 2015 #1
    Hi I was posting on io9 on a thread that asked "what scientific fact transformed the way you view the world?"

    I posted

    I got that from Brian Greene in The Elegant Universe.

    Someone responded challenging me with.

    I'm really having a hard time making sense of his reasoning and why gravity changes this. Also the term "held-still photon" isn't something I've ever come across. Maybe I shouldn't have used the phrase "arrested in time" or something. I'm not looking to one up this guy. I'd just really like this to be clarified.

    I've spent at least an hour looking into this and I'm pretty sure I'm not mistaken, but I really can't decipher this guys comment.
  2. jcsd
  3. Feb 25, 2015 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    You cannot decipher it because it does not make much sense. Light follows null geodesics regardless of the coordinate system chosen and massive objects follow time-like paths. This is an inherent property of how objects behave in space-time and has nothing to do with changing coordinates.

    Sure, you can find a coordinate system where a light signal follows a coordinate line, but this coordinate will then have a zero in the diagonal component of the metric tensor for this coordinate.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook